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, 13 (12), 1103-24

Microbially Induced Sedimentary Structures Recording an Ancient Ecosystem in the Ca. 3.48 Billion-Year-Old Dresser Formation, Pilbara, Western Australia

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Microbially Induced Sedimentary Structures Recording an Ancient Ecosystem in the Ca. 3.48 Billion-Year-Old Dresser Formation, Pilbara, Western Australia

Nora Noffke et al. Astrobiology.

Abstract

Microbially induced sedimentary structures (MISS) result from the response of microbial mats to physical sediment dynamics. MISS are cosmopolitan and found in many modern environments, including shelves, tidal flats, lagoons, riverine shores, lakes, interdune areas, and sabkhas. The structures record highly diverse communities of microbial mats and have been reported from numerous intervals in the geological record up to 3.2 billion years (Ga) old. This contribution describes a suite of MISS from some of the oldest well-preserved sedimentary rocks in the geological record, the early Archean (ca. 3.48 Ga) Dresser Formation, Western Australia. Outcrop mapping at the meter to millimeter scale defined five sub-environments characteristic of an ancient coastal sabkha. These sub-environments contain associations of distinct macroscopic and microscopic MISS. Macroscopic MISS include polygonal oscillation cracks and gas domes, erosional remnants and pockets, and mat chips. Microscopic MISS comprise tufts, sinoidal structures, and laminae fabrics; the microscopic laminae are composed of primary carbonaceous matter, pyrite, and hematite, plus trapped and bound grains. Identical suites of MISS occur in equivalent environmental settings through the entire subsequent history of Earth including the present time. This work extends the geological record of MISS by almost 300 million years. Complex mat-forming microbial communities likely existed almost 3.5 billion years ago.

Figures

<b>FIG. 1.</b>
FIG. 1.
Examples of modern microbially induced sedimentary structures (MISS). (A) Sinoidal structure visible in vertical section of a modern sediment (sabkha Bahar Alouane, Tunisia, 1996). The dark laminae are biofilms that originally covered the crests and valleys of ripple marks that once were located on top of the sedimentary surface. The ripple marks are now buried, but the organic matter of their biofilm coating is still visible. Scale: 1 cm. (B) Erosional remnants and pockets. The surface of the tidal flats of Mellum Island, Germany (September 1994), is arranged into elevated surface portions overgrown by microbial mats. In the deeper surface portions the sediment is exposed and rippled by the flood currents. Scale: 1 m. The insert shows the edge of an erosional remnant along which the microbial mat is hanging down like a tissue. The sediment originally beneath the fringed edge of the microbial mat was eroded away by currents. This erosion along the erosional remnants broadens the erosional pockets. The erosive current also may rip off individual, centimeter-scale fragments from the fringed microbial mat margin. Scale: knife, 10 cm. (C) Polygonal oscillation cracks. During seasons of sustained aridity, microbial mats dry and shrink. Polygons of microbial mat form, each separated by a crack exposing the sediment beneath the microbial mat. The image shows the first generation of polygons of microbial mat still early in the year; the mat is not yet dense enough to trap gas beneath and to cause gas domes. Portsmouth Island, North Carolina, USA (September 2005). Scale: 1 m. (D) Honeycomb pattern of tufts and ridges, lateral view. This close-up shows the triangular tufts oriented perpendicular to the microbial mat surface. These tufts are composed of filamentous cyanobacteria that move along each other in an upward direction, a migration probably coordinated by cell-cell communication and quorum sensing. Sabkha Bahar Alouane, Tunisia (1996). Scale: 0.5 cm.
<b>FIG. 2.</b>
FIG. 2.
Location and stratigraphic setting of the Dresser Formation. (A) The Dresser Formation outcrops in a roughly circular pattern in the North Pole Dome area, Pilbara Craton, Western Australia (after Van Kranendonk, ; Van Kranendonk et al., 2008). (B) The Dresser Formation has an age of approximately 3.48 Ga. (C) Geographical locations of the stratigraphic sections studied (details in Fig. 3).
<b>FIG. 3.</b>
FIG. 3.
Stratigraphic sections studied, 3.48 Ga Dresser Formation, Pilbara, Western Australia. (A) to (H) Detailed stratigraphic profiles documenting lithology and sedimentary structures. Where the lithology could not be determined anymore the signature was left blank.
<b>FIG. 3.</b>
FIG. 3.
Stratigraphic sections studied, 3.48 Ga Dresser Formation, Pilbara, Western Australia. (A) to (H) Detailed stratigraphic profiles documenting lithology and sedimentary structures. Where the lithology could not be determined anymore the signature was left blank.
<b>FIG. 4.</b>
FIG. 4.
Sedimentary structures typical in the Dresser Formation, Pilbara, Western Australia. (A) Wave ripple marks on a bed surface tilted about 30° toward the observer. Scale: 10 cm. (B) Ripple cross stratification in vertical section of a rock bed. Note dark laminae, of which examples are magnified in Fig. 5. (C) Tidalites forming a vertical stack of layers. Scale: 0.5 cm. (D) Oncoids in thin section. Scale: 0.25 mm.
<b>FIG. 5.</b>
FIG. 5.
Crinkled laminae and tufts in microscopic view (thin sections), subtidal zone, 3.48 Ga Dresser Formation, Pilbara, Western Australia. (A) Sketch to point out the situation of the thin section displayed in (B). The thin section shows an area of a vertical cut through ripple marks with their ripple valleys being filled in by sediment. The selected area covers one slope of a ripple mark and about half the ripple valley. Compare this photo also with Fig. 1A. (B) Thin-section view of the area shown in (A). The slope of the ripple mark is draped by a dark lamina (arrow); the horizontal sediment layers that fill in the ripple valley are each covered by a dark lamina as well. Scale: 0.1 cm. Note that none of the dark laminae show any mark of erosion. (C) In close-up the dark laminae include tufted microstructures (compare with modern structure in Fig. 1D; geochemistry of fossil example is shown in Fig. 6). Scale: 50 μm.
<b>FIG. 6.</b>
FIG. 6.
Tufted microstructures of the subtidal zone, 3.48 Ga Dresser Formation, Pilbara, Western Australia. (A) Thin section photomicrograph taken perpendicular to bedding showing a series of linked tufts. Arrow indicates the tuft analyzed in (B–C). (B) Optical image plus Raman chemical maps of a single tuft showing that the tuft is composed of quartz, pyrite, and significant amounts of carbonaceous matter. (C) Typical Raman spectra from two carbonaceous areas of the tuft show the presence of pyrite (P) and quartz (Q) plus two carbon peaks (C) at ∼1350 cm−1 (the “D1” disordered peak) and ∼1600 cm−1 (the “G” graphite peak). The D1 and G peak positions and widths, plus the D1/G peak heights and areas, are characteristic of thermally mature but disordered organic carbon that has experienced prehnite-pumpellyite to greenschist facies metamorphism (Beyssac et al., 2002). This degree of maturation is consistent with the known metamorphic grade of the Dresser Formation (Van Kranendonk et al., 2008) and indicates that the carbon is probably indigenous to these rocks.
<b>FIG. 7.</b>
FIG. 7.
Macrostructures of the intertidal zone, 3.48 Ga Dresser Formation, Pilbara, Western Australia, plus possible modern equivalents. The center images show the Dresser Formation structures; for better visualization, the Dresser structures are outlined in the sketches on the left. The right images show possible modern counterparts of such structures. (A) Flat fragments deposited at random on the sedimentary surface in the Dresser intertidal flats. In equivalent modern settings, such fragments represent microbial mat chips; example from Portsmouth Island, USA. Such chips were ripped off their parent site along fringed edges of microbial mats, similar to those shown in the insert of Fig. 1B. (B) Rolled-up fragment. In modern settings, microbial mat chips can be rolled up in this fashion by currents or by desiccation; example from Portsmouth Island, USA. (C) upward-bent, dark-colored sediment lamina. In modern environments, such laminae represent microbial mats separated from their substrate by erosion; example from El Bibane, Tunisia. All scales: 1 cm.
<b>FIG. 8.</b>
FIG. 8.
Fragments accumulated as piles in the intertidal zone, 3.48 Ga Dresser Formation, Pilbara, Western Australia, plus possible modern equivalents. (A) Left: fossil fragments. Right: In the modern intertidal zone of Portsmouth Island, USA, microbial mat chips were accumulated by water currents. (B) Left: Three fragments are accumulated as a pile; two fragments were deposited individually; Dresser Formation. Right: a similar situation in the modern intertidal zone of Portsmouth Island, USA. All scales: 1 cm.
<b>FIG. 9.</b>
FIG. 9.
Macrostructures of the lower supratidal zone, 3.48 Ga Dresser Formation, Pilbara, Western Australia, plus possible modern equivalents. The center images show the Dresser Formation structures; for better visualization, the Dresser structures are outlined in the sketches on the left. The right images show possible modern counterparts of such structures. (A) Fragments deposited along the edge of an erosive margin. One fragment is deposited on top of the elevated, planar surface of the eroded margin; the other fragment is situated close to its original parent site at the edge of the erosive margin. In modern settings, such erosive margins with irregular edges are caused by partial erosion of microbial mat-stabilized surfaces (compare the example shown in the insert of Fig. 1B). The irregular shape of the fossil fragments supports the interpretation as a possible mat chip. Note that the microbial mat-covered sediment is elevated (=erosional remnant). In contrast, sediment bare of microbenthos is deeper lying (=erosional pocket; compare with Fig. 10); modern example from Mellum Island, Germany. Scale: 1 cm. (B) Wrinkled upper surface of a rock bed. In modern environments, such wrinkle structures are typical for surfaces of EPS-rich microbial mats; modern example from Mellum Island, Germany. Scale: 1 cm. (C) Sedimentary rock surface arranged into polygons. Many polygons have a hole in their center. In modern settings, such polygons form within microbial mats exposed to seasonal changes of humidity. They are called polygonal oscillation cracks. Each individual polygon is separated from its neighbors by a 3–10 cm wide transition zone (desiccation cracks, often overgrown by a younger generation of microbial mat). The holes in each of the polygons are collapsed gas domes (compare Figs. 1C and 14); modern example from El Bibane, Tunisia. Scale: 10 cm. (D) Honeycomb pattern of ridges and tufts exposed on a surface of a sedimentary rock bed. In modern settings, such ridges arranged into a honeycomb pattern are typical for microbial mats developing in tidal pools. Meeting points of ridges are marked by tufts; example from Portsmouth Island, USA. Scale: 5 cm. (Compare Fig. 1D.) (E) Dark-light laminae forming a stack in possibly lagoonal sedimentary rocks. In modern settings, such laminae become visible in vertical section through very mature microbial mats. The laminae represent many layers of succeeding microbial mat generations, or microbial mat-overgrown lagoon sediments. Stacks of mat laminae are called biolaminites. Millimeter-scale mat chips and roll-ups occur within laminae (compare Fig. 17, geochemistry in Fig. 18); modern example from El Bibane, Tunisia. Scale: 5 cm.
<b>FIG. 10.</b>
FIG. 10.
Macroscopic sedimentary structures of the lower supratidal zone, 3.48 Ga Dresser Formation, Pilbara, Western Australia. (A) Three generations of erosive margins (numbers 1 to 3). Scale: 5 cm. (B) Edge of an erosive margin in close-up. Scale: 5 cm. (C) Fragments deposited in front of an erosive margin. (Compare Figs. 1B and 10A.) Tape for scale.
<b>FIG. 11.</b>
FIG. 11.
Photomicrograph of thin section perpendicular through fragment, lower supratidal zone, Dresser Formation, Pilbara, Western Australia. Dark laminae (filamentlike textures) form a carpetlike network in which individual sedimentary grains are interwoven. Note the diffuse appearance of each lamina, which allows only a two-dimensional interpretative sketch. Scale: 500 μm. Color images available online at www.liebertonline.com/ast
<b>FIG. 12.</b>
FIG. 12.
Morphology and geochemistry of network of laminae in sediment of the lower supratidal zone, 3.48 Ga Dresser Formation, Pilbara, Western Australia. (A) Thin-section photomicrograph of dark brown laminae forming a carpetlike network (compare to filamentlike textures in Fig. 11); box in (A) is enlarged in (B); boxed area in (B) indicates area analyzed by Raman in (C) to (E). (C) Raman chemical maps of part of filamentous texture showing that it is composed of hematite and organic carbonaceous matter enclosed within a matrix of quartz. The hematite map was produced using the ∼415 cm−1 hematite Raman peak, the quartz map using the ∼465 cm−1 Raman quartz peak, and the carbon map using the ∼1600 cm−1 Raman carbon peak. (D) Raman spectrum from an area of the filamentous texture rich in hematite (H) and carbon (C) showing the typical peaks for each mineral. Note that carbon and hematite both have major peaks in the 1320–1350 cm−1 region, so the presence of organic carbon must be confirmed and mapped using the 1600 cm−1 peak (Rividi et al., ; Marshall et al., 2011). Carbonate (labeled “Carb”) is occasionally found in the vicinity of these filamentous textures. (E) Raman spectrum from hematite-rich area lacking organic carbon. Note absence of carbon 1600 cm−1 peak. Unlabeled peaks in (D–E) are from the quartz matrix.
<b>FIG. 13.</b>
FIG. 13.
Laminae forming a network typical for microbial mats as seen in thin sections; Archean, Proterozoic, and Phanerozoic (including modern) examples are compared with each other. On the left side, networks of filamentlike textures (laminae) of various ages are compared with each other, starting at the base with the oldest, the Dresser Formation, and continuing upward with younger examples. On the right, rose diagrams summarize the alignment of laminae defining the networks; note that the networks of all periods of Earth history studied show a very similar dumbbell shaped pattern (right; n=number of thin sections studied). Also, the thin sections deriving from the Dresser sedimentary rocks display similar network patterns; compare Fig. 12 for their geochemistry. In contrast, abiotic laminae of a stylolite preserved in the 2.9 Ga Pongola Supergroup, South Africa, are shown in the lower portion of the figure. Note that the stylolite resulted in a different alignment pattern of laminae (from Noffke et al., 2008).
<b>FIG. 14.</b>
FIG. 14.
Polygonal oscillation cracks on sedimentary surfaces viewed from above, fossil and modern examples. (A) This polygon is defined by its slightly elevated margin. The close-up view allows recognition of a fossil gas escape hole in its center; Dresser Formation, Pilbara, Western Australia. Scale: 3 cm. (B) For comparison to (A), this image shows a very similar structure representing an ancient gas escape hole; 2.9 Ga Pongola Supergroup, South Africa. Scale: 5 cm. (C) A single polygon of a microbial mat from the sabkha El Bibane, Tunisia (modern). Note the circularly wrinkled folds within the microbial mat polygon, especially close to the tip of the pen. (D) A single polygon from the Dresser Formation, Pilbara, Western Australia. Note the presence of very similar circularly wrinkled folds. Scale: 4 cm. Compare Fig. 1C for further modern examples and Fig. 15 for statistical measurements.
<b>FIG. 15.</b>
FIG. 15.
Comparative morphologies of polygonal oscillation cracks from the 3.48 Ga Dresser Formation, the 2.9 Ga Pongola Supergroup, and El Bibane, Tunisia (modern). The frequency distributions of the polygon diameter/gas hole diameter are similar in all three cases. Dresser Formation polygons are 10–20 cm wide, 2.9 Ga Pongola Supergroup examples are 20–50 cm wide, and examples from the modern sabkha of Tunisia are 15–50 cm wide. In the Dresser Formation, the gas escape holes have a diameter of 1–3 cm, and the comparable younger structures show diameters of 3–10 cm, occasionally up to 15 cm. Examples for such structures are shown in Fig. 14. Color images available online at www.liebertonline.com/ast
<b>FIG. 16.</b>
FIG. 16.
Comparison of honeycomb-like patterns of ridges and tufts on surfaces of microbial mats from the 3.48 Ga Dresser Formation, the 2.9 Ga Pongola Supergroup, and El Bibane, Tunisia (modern). The ratio between three generations of compartments is approximately 4:1 for each of the three modal peaks across all examples studied. Compare the structures shown in Fig. 9D. Color images available online at www.liebertonline.com/ast
<b>FIG. 17.</b>
FIG. 17.
Fragments in possible lagoonal deposits, microphotograph of thin section; 3.48 Ga Dresser Formation, Pilbara, Western Australia. Note the wavy appearance of the fragments. One fragment is rolled up. Geochemistry is shown in Fig. 18. Scale: 0.5 cm.
<b>FIG. 18.</b>
FIG. 18.
Geochemistry of sedimentary fragments (see Fig. 17) in lagoonal deposits, 3.48 Ga Dresser Formation, Pilbara, Western Australia. (A) Vertical section through a typical fragment in petrographic thin section. Boxed area enlarged in (B). (B) Higher magnification view of fragment with the area analyzed using Raman indicated by the box. (C) Raman maps showing the mineralogical composition of the fragment. The goethite map was produced using the ∼400 cm−1 goethite Raman peak, the quartz map using the ∼465 cm−1 Raman quartz peak, and the carbon map using the ∼1600 cm−1 Raman carbon peak. (D) A typical Raman spectrum from a carbonaceous area within the fragment. This image shows background quartz (Q) and goethite (G) peaks, together with the ∼1350 and ∼1600 cm−1 carbon peaks (C) that are characteristic of thermally mature but disordered organic carbon.

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